Every compressor has an instability zone in which it must not operate. Consequently, the control devices of these compressors include an anti-surge valve equipped with a servomotor and connected between the outlet and inlet of the compressor.
The servomotor of such an anti-surge valve is controlled by regulating means which receive at the input a parameter representing the flow of the compressor and a nominal value determined from the inlet pressure and outlet pressure of the compressor, for the purpose of injecting some of the outlet flow of the compressor at its inlet, in order to keep the compressor above its breakaway point.
However, prior art devices have disadvantages, because the anti-surge valves have a very long response time and the incursions of the compressor on either side of its nominal operating point are relatively pronounced and can cause the compressor to go past its breakaway point and reach a state of instability, and it is then impossible to return it to normal operation without stopping it.
Prior art solutions involve shifting the safety curve of the compressor so as to move it away from its instability zone, to prevent the incursions on either side of its nominal operating point from causing the compressor to cross its breakaway point.
This solution is not very satisfactory, inasmuch as the powers of compressors tend to increase more and more and/or their response times have to be as short as possible. Moreover, these devices are also limited by the stability of the regulating means.